1. Field of the Invention
The invention relates to a conveying device for collecting and transporting printed sheets placed astraddle on a first chain conveyor which printed sheets are gripped by an intermediate conveying device at the end of the collecting process on the first chain conveyor and then transported and transferred to a second chain conveyor or conveying device arranged downstream and synchronized with the first chain conveyor.
2. Description of the Related Art
Conveying devices of this kind are known inter alia in gather stitcher devices on which printed sheets are stitched at the end of a collecting process. It is moreover known to arrange two or more gather stitchers in series to be able to produce voluminous printed products wherein the final stitching action is carried out by the stitching station of the last gather stitcher in line while the stitching stations of the preceding gather stitchers are switched off. This combination of gather stitchers requires intermediate conveying devices between two gather stitchers which transport the intermediate products at the end of the collecting process on a first chain conveyor of a gather stitcher to a second chain conveyor of the successive gather stitcher, respectively.
A conveying device of this kind is disclosed in Japanese patent document JP-A-8/143179. The printed sheets which are collected on a first chain conveyor in the form of intermediate products positioned astraddle on the chain conveyor are moved by followers fastened on a circulating traction mechanism from the first chain conveyor via a stationary profiled guide rail onto a second chain conveyor. The guide rail projects with its ends into the conveying areas that are formed by the chain conveyors; the inlet area of the second chain conveyor requires a device which opens the intermediate products so that an interruption-free transfer is ensured.
Pushing the intermediate products on the trailing edge has several disadvantages. When the intermediate product is comprised of thin sheets, the trailing edge can be damaged by the impact of the follower provided for pushing, in particular, in the case of intermediate products that are heavy or have insufficient gliding properties, and this can impair the further processing of the intermediate products. Also, the transfer onto the second chain conveyor is complex in the case of intermediate products comprised of thin sheets. Pushing of relatively heavy intermediate products can cause markings or damage of the printed image at the inner edge of the fold.
In particular, the known intermediate conveying device is not suitable when the intermediate conveying stretch is curved or bent because pushing of an intermediate product at the trailing edge can result in deformations within the fold area which can cause disruptions during further processing.
These conditions represent impairments in regard to being able to provide an arrangement of the gather stitchers that deviates from the row-like, straight arrangement of several chain conveyors for the purpose of an optimal spatial distribution and arrangement.
It is an object of the present invention to provide a conveying device of the aforementioned kind in which the printed products are safely guided in the area of the intermediate conveying device and which makes it possible to connect two chain conveyors such that they have different conveying directions.
In accordance with the present invention, this is achieved in that the intermediate conveying device for gripping the intermediate products formed at the end of the collecting process on the first chain conveyor comprises controllable grippers which are connected to a circulating traction mechanism and grip the intermediate products, lifted off the first chain conveyor, in the area of the fold and transport them in an open position to the second chain conveyor.
In this way, the printed products are no longer pushed by followers between two chain conveyors but are gripped and guided by grippers and in this way transported from the first chain conveyor to the second chain conveyor. It would also be possible to provide, instead of the second chain conveyor, other continuously operating conveying devices which transport the intermediate products over sections of the transport stretch.
When according to a further embodiment of the invention the intermediate conveying device in the form of a gripping transporter comprises an articulated chain on which the grippers are arranged, it is possible to deflect the printed products on transfer from the first to the second chain conveyor into a conveying direction which is different from the conveying direction of the first chain conveyor. For example, a deflection of  greater than 0xc2x0 up to 180xc2x0 is possible. This has the important advantage that even very long conveying devices can be installed in a space-saving way. For example, such a conveying device can be installed in a corner of a building. For a deflection by 180xc2x0, the chain conveyors of two gather stitchers can be arranged parallel to one another. The conveying device can also be installed so as to extend over several floors of a building.
A particularly stable transfer from the first chain conveyor to the intermediate conveying device is ensured when according to a further embodiment of the invention a lifting device is provided which lifts intermediate products off the first chain conveyor. Such a lifting device according to a further embodiment of the invention comprises a lifting knife which is, for example, driven so as to perform an upward swinging movement. The grippers engage the intermediate products when positioned on the lifting knife. This provides for to secure and flowing transfer from the first chain conveyor to the intermediate conveying device.
A secure guiding of the printed sheets results when according to a further embodiment of the invention the grippers engage two locations of the intermediate products, the locations being spaced apart from one another. These locations are in the vicinity of the fold, preferably at the upper edge of the intermediate products and are offset in the transport direction. The intermediate products are then gripped especially securely and cannot be displaced during a flying transfer across a gap or cannot change their position in any other way.